On-board diagnostics system

ABSTRACT

An on-board diagnostics system for an exhaust system of an internal combustion engine is disclosed. The system comprises one or more ferromagnetic materials and a means for measuring magnetic field strength. Also disclosed is a method for on-board diagnostics of a catalyst component in the exhaust system. The method comprises measuring the magnetic field strength of a ferromagnetic material located in close proximity to the catalyst component and determining whether the ferromagnetic material has been exposed to a temperature above the Curie temperature of the ferromagnetic material, as measured by a decrease in the measured magnetic field strength.

FIELD OF THE INVENTION

The invention relates to an on-board diagnostics system for an exhaust system of an internal combustion engine, and a method for on-board diagnostics of a catalyst component in the exhaust system.

BACKGROUND OF THE INVENTION

Internal combustion engines produce exhaust gases containing a variety of pollutants, including hydrocarbons, carbon monoxide, nitrogen oxides (“NO_(x)”), sulfur oxides, and particulate matter. Increasingly stringent national and regional legislation has lowered the amount of pollutants that can be emitted from such diesel or gasoline engines. Exhaust systems containing various catalyst components have been developed to attain these low emission levels.

With the increasing complexity of these exhaust systems, on-board diagnostics have been developed to allow vehicle owners to understand the operating condition of the exhaust system. On-board diagnostics (“OBD”) in the context of a motor vehicle is a generic term to describe the self-diagnostic and reporting capability of the vehicle's systems provided by a network of sensors linked to a suitable electronic management system. Early examples of OBD systems would simply illuminate a malfunction indicator light if a problem were detected, but it provided no information on the nature of the problem. More modern OBD systems use a standardized digital connection port and are capable of providing information on standardized diagnostic trouble codes and a selection of real-time data, which enable rapid problem identification and resolution of a vehicle's systems.

Besides lowering engine emissions from a vehicle, newer legislation also requires the increasing use of on-board diagnostics (OBD) to notify the driver in case of a malfunction or deterioration of the emission system that would cause emissions to exceed mandatory thresholds; e.g., a particulate matter, carbon monoxide, hydrocarbon and/or NO_(x) level above a set limit (typically in g/km of a pollutant emissions). These levels could be reached after thermal deactivation of the catalyst. See, for example, U.S. Pat. Appl. Pub. No. 2012/0216508 which teaches the incorporation of a heat sensitive oxygen storage material in a hydrocarbon trap (HC trap) material, and the use of conventional determination of OSC efficiency to determine if the HC trap material has been exposed to excessive temperature.

As with any automotive system and process, it is desirable to attain still further improvements in on-board diagnostics systems. We have discovered a new on-board diagnostics system that is capable of detecting whether a catalyst component has experienced the high aging temperatures that may cause deactivation and possible failing of OBD limits.

SUMMARY OF THE INVENTION

The invention is an on-board diagnostics system for an exhaust system of an internal combustion engine. The on-board diagnostics system comprises one or more ferromagnetic materials and a means for measuring magnetic field strength. The invention also includes a method for on-board diagnostics of a catalyst component in the exhaust system. The method comprises measuring the magnetic field strength of a ferromagnetic material located in close proximity to the catalyst component and determining whether the ferromagnetic material has been exposed to a temperature above the Curie temperature of the ferromagnetic material, as measured by a decrease in the measured magnetic field strength.

DETAILED DESCRIPTION OF THE INVENTION

The on-board diagnostics system of the invention comprises one or more ferromagnetic materials and a means for measuring magnetic field strength. Ferromagnetic materials include any material that has a large, positive susceptibility to an external magnetic field. Ferromagnetic materials become magnetized when the electron spins become aligned to an external magnetic field. They typically exhibit a strong attraction to magnetic fields and are able to retain their magnetic properties after the external field has been removed. In the scope of this invention, materials that have a net magnetization shall be considered ferromagnetic even if some electron spins are anti-aligned and reduce the overall net magnetization (sometimes referred to as ferrimagnetic materials). Therefore, the term “ferromagnetic material” as used in the scope of the invention also includes a ferrimagnetic material.

Interestingly, the magnetic effects of ferromagnetic materials are sensitive to temperature. At higher temperatures, the atoms of the ferromagnetic materials will move around more, throwing the spins out of alignment. Above a critical temperature known as the Curie temperature, ferromagnets lose their ferromagnetic properties. That is, the Curie temperature is the temperature above which a ferromagnetic material loses all of its ferromagnetic properties.

Preferably, the ferromagnetic materials useful in the invention include Fe, Fe₂O₃, Co, NiFe₂O₃, and AINiCo (an aluminum-nickel-cobalt alloy). The Curie temperature of Fe is 770° C.; Fe₂O₃ is 675° C.; Co is 1115° C.; NiOFe₂O₃ is 585° C.; and AlNiCo is about 800° C.

The on-board diagnostics system of the invention also includes a means for measuring magnetic field strength. Means for measuring magnetic field strength are well known in the art. The means for measuring magnetic field strength include magnetometers (such as a rotating coil, Hall-Effect (Gauss/Tesla) magnetometers, NMR magnetometers, SQUID magnetometers, and fluxgate magnetometers), Hall-Effect semi-conductor sensors, and Gradiometers (including axial and planar gradiometers).

These means for measuring magnetic field strength are preferably portable devices that can easily be installed on a vehicle. One particular advantage of using magnetic field strength for OBD purposes is that it can be monitored continuously, without changes to the combustion mode, and under a wide range of engine operating conditions including engine idling or when the engine is stopped.

The on-board diagnostics system of the invention is preferably used to detect the potential thermal deterioration of a catalyst component located in the exhaust system. Although any exhaust system catalyst component can be used in the invention, the catalyst component is preferably a three-way catalyst (TWC), a diesel oxidation catalyst (DOC), a lean NO_(x) trap, a catalyzed soot filter (CSF), a selective catalytic reduction (SCR) catalyst, or an SCR coated filter (SCRF).

These catalyst components are well-known in the art. The catalyst components typically comprise a catalyst coating coated on a substrate. The substrate is preferably a ceramic substrate or a metallic substrate. The ceramic substrate may be made of any suitable refractory material, e.g., alumina, silica, titania, ceria, zirconia, magnesia, zeolites, silicon nitride, silicon carbide, zirconium silicates, magnesium silicates, aluminosilicates and metallo aluminosilicates (such as cordierite and spudomene), or a mixture or mixed oxide of any two or more thereof. Cordierite, a magnesium aluminosilicate, and silicon carbide are particularly preferred.

The metallic substrate may be made of any suitable metal, and in particular heat-resistant metals and metal alloys such as titanium and stainless steel as well as ferritic alloys containing iron, nickel, chromium, and/or aluminum in addition to other trace metals.

The substrate may be a filter substrate or a flow-through substrate, depending on the application. If the substrate is a flow-through substrate, it is preferably a honeycomb monolith. The substrate is typically designed to provide a number of channels through which vehicle exhaust passes. The surface of the channels is loaded with the catalyst coating.

Three-way catalyst systems (TWCs) are typically used in gasoline engines under stoichiometric conditions in order to convert NO_(x) to N₂, carbon monoxide to CO₂, and hydrocarbons to CO₂ and H₂O on a single device. The TWC preferably comprises a combination of two or more platinum group metals (PGMs), generally Pt/Rh, Pd/Rh or Pt/Pd/Rh. The PGMs and any catalyst promoters used, e.g. a barium-based compound, are typically supported by one or both of an oxygen storage component (OSC), e.g. a Ce—Zr mixed or composite oxide, and a high surface area inorganic oxide, e.g. alumina.

Diesel oxidation catalysts (DOCs) are designed to oxidize CO to CO₂ and gas phase hydrocarbons (HC) and an organic fraction of diesel particulates (soluble organic fraction) to CO₂ and H₂O. Typical DOC components include platinum and optionally also palladium on a high surface area inorganic oxide support, such as alumina, silica-alumina and a zeolite.

A catalyzed soot filter (CSF) is a filter substrate that is coated with a catalyst of similar composition and function to a DOC. It can also assist in the combustion of diesel particulate matter. Typical CSF catalyst components include platinum, palladium, and a high surface area inorganic oxide.

Selective catalytic reduction (SCR) catalysts are catalysts that reduce NO_(x) to N₂ by reaction with nitrogen compounds (such as ammonia or urea) or hydrocarbons (lean NO_(x) reduction). A typical SCR catalyst is comprised of a vanadia-titania catalyst, a vanadia-tungsta-titania catalyst, or a metal/zeolite catalyst such as iron/beta zeolite, copper/beta zeolite, copper/SSZ-13, copper/SAPO-34, Fe/ZSM-5, or copper/ZSM-5. The SCR catalyst is typically coated onto a flow-through substrate.

Selective catalytic reduction filters (SCRF) are single-substrate devices that combine the functionality of an SCR and particulate filter. They are used to reduce NO_(x) and particulate emissions from internal combustion engines. An SCRF is formed when the SCR catalyst is coated onto a filter substrate.

Lean NO_(x) traps (or NO_(x) adsorber catalysts) are catalysts that adsorb NO_(x) under lean exhaust conditions, release the adsorbed NO_(x) under rich conditions, and reduce the released NO_(x) to form N₂. NO_(x) traps typically include a NO_(x)-storage component (e.g., Ba, Ca, Sr, Mg, K, Na, Li, Cs, La, Y, Pr, and Nd), an oxidation component (preferably Pt), and a reduction component (preferably Rh). These components are contained on one or more inorganic oxide supports.

When used to detect the thermal deterioration of the catalyst component, the ferromagnetic material will preferably be located in close proximity to the catalyst component so that the ferromagnetic material is exposed to the same temperatures as the catalyst component. Preferably, the ferromagnetic material will be located within 12 inches (30.5 cm), more preferably within 6 inches (15.25 cm) of the catalyst component, and most preferably within the catalyst component itself.

For instance, the ferromagnetic material may be located within a catalyst coating of the catalyst component. When the ferromagnetic materials are incorporated into the catalyst coating itself, the ferromagnetic materials and the washcoat composition should be selected such that they are mutually compatible and do not adversely impact the catalytic activity (for example, the ferromagnetic materials should not poison the catalytic washcoat).

When the ferromagnetic material is located within the catalyst coating, the coating will preferably be magnetized (by aligning the electron spins of the ferromagnetic material) prior to installation on the vehicle. This can be achieved by passing the finished catalyst through an external magnetic field. The magnetized catalyst may then be installed on a vehicle and the magnetic field monitored using a suitable portable means for measuring the magnetic field strength.

Also, the ferromagnetic material may be located on a separate probe located within a channel of the catalyst component. It may also be located on a separate probe in close proximity of the catalyst component, preferably within 12 inches (30.5 cm), and more preferably within 6 inches (15.25 cm), of the catalyst component. When located in close proximity of the catalyst component, the separate probe is preferably located downstream of the catalyst component, such that the exhaust gas first contacts the catalyst component prior to contacting the separate probe.

When the ferromagnetic material is located on a separate probe, the probe will preferably be magnetized prior to installation on the vehicle. This can be achieved by passing the probe through an external magnetic field. The magnetized probe may then be installed on a vehicle and the magnetic field monitored using a suitable means for measuring the magnetic field strength.

The means for measuring magnetic field strength is preferably located such that it is in close enough proximity to the ferromagnetic material to measure the magnetic field strength, preferably within 12 inches (30.5 cm), and more preferably within 6 inches (15.25 cm), of the ferromagnetic material. The means for measuring magnetic field strength may be measured continuously, and if the magnetic field strength falls below a pre-determined value this would trigger a malfunction indicator light (MIL) to indicate the catalyst component had exceeded a deactivating temperature condition.

The invention also encompasses a method for on-board diagnostics of a catalyst component in an exhaust system for an internal combustion engine. The method comprises measuring the magnetic field strength of a ferromagnetic material that is located in close proximity of the catalyst component, wherein the ferromagnetic material has a Curie temperature above which the ferromagnetic material loses its ferromagnetic properties.

Preferably, the ferromagnetic material will be located within 12 inches (30.5 cm), more preferably within 6 inches (15.25 cm) of the catalyst component, and most preferably within the catalyst component itself. Preferably, the ferromagnetic material may be located within a catalyst coating of the catalyst component, as previously described. The ferromagnetic material may also preferably be located on a separate probe located within a channel of the catalyst component, or on a separate probe in close proximity of the catalyst component, as previously described. When located in close proximity of the catalyst component, the separate probe is preferably located downstream of the catalyst component, such that the exhaust gas first contacts the catalyst component prior to contacting the separate probe.

The method then comprises determining whether the ferromagnetic material has been exposed to a temperature above its Curie temperature, as measured by a decrease in the magnetic field strength. A decrease in the magnetic field strength, or a measured magnetic field strength that is zero or almost zero, indicates that the ferromagnetic material has been exposed to a high temperature above its Curie temperature. This can be used to determine if the catalyst component has been thermally deactivated by exposure to excessive temperature.

For instance, if the catalyst component is susceptible to high temperature deactivation above a certain temperature, the ferromagnetic material can be specifically chosen according to its Curie temperature. For instance, if a diesel oxidation catalyst (DOC) within the exhaust system is susceptible to deactivation when exposed to temperatures above 770° C., the ferromagnetic material useful to show deactivation of the DOC will preferably be Fe (having a Curie temperature of 770° C.).

That is, at temperatures below 770° C., the Fe ferromagnetic material will still exhibit magnetic properties as measured by, e.g., a Gauss magnetometer. The measured magnetic field will indicate that the DOC has not been exposed to a deactivating high temperature. However, at temperatures above 770° C., the Fe will lose its magnetic properties as indicated by the lack of a magnetic field measured by the magnetometer. Therefore, the DOC has been exposed to a potentially deactivating high temperature above 770° C. When the means for measuring magnetic field strength shows a loss of magnetic field, an OBD sensor may be triggered to indicate high temperature deactivation of the catalyst component.

Thus, the method of the invention further comprises triggering a malfunction indicator light when the magnetic field strength decreases below a pre-determined value, such as when the magnetic field strength approaches zero.

The following examples merely illustrate the invention. Those skilled in the art will recognize many variations that are within the spirit of the invention and scope of the claims.

EXAMPLE OF THE INVENTION

A diesel oxidation catalyst according to the invention is prepared by the following method. Appropriate amounts of platinum and palladium salts are added to alumina by the incipient wetness method. The material is dried and then calcined at 500° C. The calcined material is then slurried in water and milled to a particle size d90<20 micron. Beta zeolite is added to the slurry such that 10% of the total solids content by mass is beta zeolite. Low particle size iron particles (d90<20 micron) are added to the PGM/beta zeolite slurry and the mixture is stirred in order to homogenize it. The resulting milled slurry is applied to a cordierite flow-through monolith substrate using established coating techniques. The catalyst-containing substrate is dried and calcined at 500° C. to produce the diesel oxidation catalyst (DOC).

The DOC is then placed in an external magnetic field of appropriate field strength to magnetize the coating. The magnetized DOC catalyst is installed on a vehicle together with a magnetometer in close proximity to the catalyst canning. The magnetic field strength is continually monitored during the DOC use to diagnose whether the diesel oxidation catalyst will exceed OBD emission thresholds. After high temperature exposure (in this case at a temperature >770° C.), the magnetic field strength of the catalyst decreases significantly and would trigger a malfunction indicator light (MIL) warning on the vehicle dashboard. 

I claim:
 1. An on-board diagnostics system for an exhaust system of an internal combustion engine, the system comprising one or more ferromagnetic materials and a means for measuring magnetic field strength.
 2. The on-board diagnostics system of claim 1 wherein the ferromagnetic material is selected from the group consisting of iron, Fe₂O₃, Co, NiOFe₂O₃, AlNiCo, and alloys thereof.
 3. The on-board diagnostics system of claim 1 wherein the means for measuring magnetic field strength are selected from the group consisting of magnetometers, Hall-Effect semi-conductor sensors, and Gradiometers.
 4. The on-board diagnostic system of claim 1 wherein the ferromagnetic material is located in close proximity to a catalyst component in the exhaust system.
 5. The on-board diagnostic system of claim 4 wherein the ferromagnetic material is located within a catalyst coating of the catalyst component.
 6. The on-board diagnostic system of claim 4 wherein the ferromagnetic material is located on a separate probe located within a channel of the catalyst component or on a separate probe in close proximity of the catalyst component.
 7. The on-board diagnostic system of claim 6 wherein the separate probe in close proximity of the catalyst component is downstream of the catalyst component.
 8. The on-board diagnostics system of claim 4 wherein the catalyst component comprises a three-way catalyst, a diesel oxidation catalyst, a lean NO_(x) trap, a selective catalytic reduction (SCR) catalyst, a catalyzed soot filter, or an SCR coated filter.
 9. A method for on-board diagnostics of a catalyst component in an exhaust system for an internal combustion engine, the method comprising: (a) measuring the magnetic field strength of a ferromagnetic material that is located in close proximity to the catalyst component, wherein the ferromagnetic material has a Curie temperature above which the ferromagnetic material loses its ferromagnetic properties; and (b) determining whether the ferromagnetic material has been exposed to a temperature above the Curie temperature of the ferromagnetic material, as measured by a decrease in the measured magnetic field strength.
 10. The method of claim 9 wherein the ferromagnetic material is located within a catalyst coating of the catalyst component.
 11. The method of claim 9 wherein the ferromagnetic material is located on a separate probe located within a channel of the catalyst component or on a separate probe in close proximity of the catalyst component.
 12. The method of claim 11 wherein the separate probe in close proximity of the catalyst component is downstream of the catalyst component.
 13. The method of claim 9 further comprising triggering a malfunction indicator light when the magnetic field strength decreases below a pre-determined value. 